1. Field of the Invention
The present invention relates to mesoporous silica particles having various sizes and a method of preparing the same.
2. Description of the Related Art
Mesoporous silica is one kind of mesoporous molecular sieve. This is a mesoporous molecular sieve in which pores having a uniform size are regularly arranged. A new family of mesoporous molecular sieve materials, designated as M41S, which were synthesized using an ionic surfactant as a structure-directing agent by researchers at Mobil in 1991, are disclosed in U.S. Pat. Nos. 5,057,296 and 5,102,643. Ever since, the mesoporous molecular sieve materials have been used in various application fields, and thorough research thereon is being conducted all over the world.
Unlike the synthesis of conventional molecular sieves, the mesoporous molecular sieves are synthesized through a liquid-crystal templating mechanism, which is advantageous because the types of surfactant serving as a templating material or the synthesis conditions in the synthesis route are controlled, thereby making it possible to adjust the pore size to 1.6˜10 nm.
U.S. Pat. Nos. 6,027,706 and 6,054,111 disclose mesoporous materials prepared using amphiphilic block copolymers as nonionic surfactants. In the case of zeolite, a monomolecular inorganic or organic material generally acts as a templating material for inducing a pore structure, while, in the case of a mesoporous material, a micelle structure, in which multiple surfactant molecules are assembled, is used to induce pores, instead of the monomolecular material. The surfactant, consisting generally of a hydrophilic head portion and a hydrophobic tail portion, is known to constitute various self-assembled micelle and liquid-crystal structures in the presence of an aqueous solution. Located at the surface of the micelle or liquid-crystal structure, the hydrophilic portion interacts with an inorganic precursor to form an organic/inorganic nanocomposite, from which the surfactant is then removed, thus attaining the mesoporous material. The mesoporous material may have a pore size increased to the mesopore range (2˜10 nm), compared to conventional microporous materials having a pore size of 1.5 nm or less, such as zeolite or AlPO-based materials, thereby enabling the application of molecular sieve materials to fields in which the application thereof has been limited until now, for example, adsorption and separation of molecules having a larger pore size than microporous materials, and catalytic conversion reactions. The mesoporous material having regular pores has a very large surface area (>700 m2/g) and thus exhibits superior properties that are able to adsorb atoms or molecules. Further, because the mesoporous material has a uniform pore size, it is used as the carrier of catalyst activators, such as transition metal compounds or amine-based oxides. Furthermore, the mesoporous material is expected to be applied as conductive materials, optical display materials, chemical sensors, fine chemicals and bio-powders, novel insulators having mechanical or thermal properties, and packaging materials, and to have many applications.
To date, research into the synthesis of spherical mesoporous silica nanoparticles smaller than 1 μm and control of the morphology thereof has been extensively conducted to elucidate special physical and chemical properties. However, mesoporous silica particles having a particle size of 10 μm or more are almost impossible to synthesize through the method based on the Stöber process, which is used to synthesize conventional mesoporous particles. On the other hand, few study results on synthesis of mesoporous silica particles larger than 100 μm have been reported [H.-P. Lin and C.-Y. Mou, Acc. Chem. Res., 2002, 35, 927; C.-P. Kao, H.-P. Lin and C.-Y. Mou, J. Phys. Chem. Solids. 2001, 62, 1555].
Further, methods of synthesizing mesoporous silica particles having a size of 30˜50 μm have recently been reported [K. Kosuge and P. S. Singh, Chem. Mater., 2001, 13, 2476]. However, because the synthesized mesoporous silica has a mesopore diameter smaller than 4 nm, many problems may occur when active materials are introduced from the outside.
Although various synthesis methods for adjusting the pore size through the introduction of an organic additive, such as a hydrocarbon, alcohol, or ether, as a swelling agent are known, it is still difficult to prepare silica having mesopores larger than 10 nm using an organic template. Hence, studies on methods of increasing the mesopore size are urgently required.
These days, mesoporous silica, MCM-41, having a very large pore size, is synthesized by introducing N,N-dimethyldecylamine as a swelling agent for increasing pore size [A. Sayari, S. Hamoudi and Y. Yang, Chem. Mater., 2005, 17, 212]. However, the above synthesis method suffers because it has a complicated preparation process and cannot increase the pore size beyond 30 nm.